1. Field of the Invention
The present invention relates to an optical disc for storing information by irradiating laser light onto an optical disc medium, and an optical disc device for same.
2. Description of the Related Art
In recent years, great developments have been made in optical disc devices as means for storing and reproducing large volumes of data, and approaches for achieving high storage density have been adopted, one of these methods being a phase change-type optical disc device utilizing reversible crystalxe2x80x94non-crystal state changes.
In a phase change-type optical disc device, marks (amorphous sections) and spaces (crystalline sections) between these marks are formed on an optical disc medium, by irradiating semiconductor laser light onto the optical disc medium using two power settings: a peak power for rendering crystalline regions amorphous, and a bias power for crystallizing amorphous regions.
Land/groove recording technology exists for recording these marks and spaces in tracks in both the land region and the groove region of a guide groove on a disc.
In order to improve the reliability of optical discs, it is necessary to store and reproduce high-quality signals on the optical disc. If there is an inclination (tilt angle) of the recording surface of an optical disc with respect to the optical axis of the light beam, then an aberration occurs in the light spot and it becomes difficult to record and reproduce high-quality signals on the optical disc. Therefore, in order to record and reproduce signals to and from the optical disc, it is necessary to detect the aforementioned tilt angle accurately, and to correct this tilt angle.
A conventional method for correcting tilt by a tilt device is shown in FIG. 2.
In FIG. 2, 201 is an optical disc, 202 is an optical head which focuses a light beam onto the optical disc, 203 is a tilt platform, 204 is a signal calculating circuit, 205 denotes focus control means for controlling the focal position of the light spot on the optical disc surface, 206 denotes tracking control means for controlling the position of the optical spot on the track, 207 is a tilt sensor for irradiating light for detecting the inclination of the optical disc signal with respect to the optical axis of the aforementioned optical beam, onto the optical disc, receiving light reflected by the optical disc, and detecting the inclination of the recording surface of the optical disc with respect to the optical axis of the aforementioned light beam, and 208 denotes tilt control means for controlling the inclination of the recording surface of the aforementioned optical disc with respect to the optical axis of the aforementioned light beam, by inclining the aforementioned tilt platform according to the value detected by the aforementioned tilt sensor.
FIG. 3 shows a graph of a case where the tilt position is corrected at both the inner circumference and outer circumference of the optical disc, in a conventional optical disc device.
However, in the conventional composition, since a tilt sensor and tilt controlling means as illustrated in FIG. 2 are used to detect the tilt position of the optical disc, it has been necessary to provide a tilt sensor 207 for detecting tilt, separately from the optical head 202, in order to correct the inclination of the recording surface of the optical disc with respect to the optical axis of the optical beam. The incorporation of two optical systems in the optical head and the tilt sensor makes the optical disc device more complex, increases the space occupied by the device, and leads to cost rises. Moreover, the optical axes of the two optical systems in the optical head and the tilt sensor must be adjusted, and therefore adjustment tasks become more complex, and errors are liable to occur between the tilt sensor and the inclination (tilt angle) of the recording surface of the optical disc with respect to the optical axis of the aforementioned optical beam, making it difficult to detect the tilt angle accurately.
The present invention overcomes all of the aforementioned problems, an object thereof being to improve the quality of the light spot and recording and reproduction characteristics by correcting the inclination of the optical disc with respect to the optical axis of the light beam at radial positions at the inner circumference, middle circumference and outer circumference of the optical disc, in such a manner that the value detected by the tilt detecting means is a suitable value.
In order to resolve the aforementioned problems, the present invention comprises the following aspects.
The first aspect of the invention corresponds to method (1) in the embodiments.
The first aspect is a tilt detection device for detecting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
a two-split photo detector for receiving light reflected from said optical disc, said photo detector including a first photo detecting element and a second photo detecting element divided in a direction parallel to the track;
tracking control means for controlling the position of said light spot on a track; and
tilt detecting means for detecting inclination of the recording surface of the optical disc with respect to the optical axis of said light beam by a difference signal output representing the difference between the signals from said first and second photo detecting elements when reflected light from said continuous track is received by the two-split photo detector.
Thereby, it is possible to improve signal quality during recording and reproduction, by detecting the tilt angle by pits recorded previously in the optical disc, without needing to provide an optical system for detecting the tilt angle separately from the optical system for recording and reproducing signals. Consequently, this has the effect of reducing the installation size of the device and lowering costs.
The second aspect of the invention corresponds to method (4) in the embodiments.
The second aspect is a tilt detection device detecting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
a two-split photo detector for receiving light reflected from said optical disc, said photo detector including a first photo detecting element and a second photo detecting element divided in a direction parallel to the track;
tracking control means for controlling the position of said light spot on a track; and
tilt detecting means for detecting inclination of the recording surface of the optical disc, by comparing a first summed signal representing the sum of the outputs from the first and second photo detecting elements when reflected light from said first shifted pits is received by the two-split photo detector, with a second summed signal representing the sum of the outputs from the first and second photo detecting elements when reflected light from said second shifted pits is received by the two-split photo detector.
The third aspect of the invention corresponds to method (4) in the embodiments, and in particular, to the lower signal level illustrated in FIGS. 21A, 21B and 21C.
The third aspect is the tilt detection device according to the second aspect of the invention, wherein said tilt detecting means compares the lower level of the:absolute value of the envelope signal of the first summed signal with the lower level of the absolute value of the envelope signal of the second summed signal.
The fourth aspect of the invention corresponds to method (4) in the embodiments, and in particular, to the upper signal level illustrated in FIGS. 21A, 21B and 21C.
The fourth aspect is the tilt detection device according to the second aspect of the invention, wherein said tilt detecting means compares the upper level of the absolute value of the envelope signal of the first summed signal with the upper level of the absolute value of the envelope signal of the second summed signal.
The fifth aspect of the invention corresponds to method (4) in the embodiments, and in particular, to the amplitude illustrated in FIGS. 21A, 21B and 21C.
The fifth aspect is the tilt detection device according to the second aspect of the invention, wherein the tilt detecting means compares the amplitude of the first summed signal with the amplitude of the second summed signal.
The sixth aspect of the invention corresponds to method (5) in the embodiments.
The sixth aspect is a tilt detection device for detecting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
a two-split photo detector for receiving light reflected from said optical disc, said photo detector including a first photo detecting element and a second photo detecting element divided in a direction parallel to the track;
tracking control means for controlling the position of said light spot on a track; and
tilt detecting means for detecting inclination of the recording surface of the optical disc, by comparing a first difference signal representing the difference between the outputs from the first and second photo detecting elements when reflected light from said first shifted pits is received by said two-split photo detector, with a second difference signal representing the difference between the outputs from the first and second photo detecting elements when reflected light from said second shifted pits is received by said two-split photo detector.
The seventh aspect of the invention corresponds to method (5) in the embodiments, and in particular, to the lower signal level illustrated in FIGS. 22A, 22B and 22C.
The seventh aspect is the tilt detection device according to the sixth aspect of the invention, wherein the tilt detecting means compares the upper level of the absolute value of the envelope of the first difference signal with the upper level of the absolute value of the envelope of the second difference signal.
The eighth aspect of the invention corresponds to method (5) in the embodiments, and in particular, to the amplitude illustrated in FIGS. 22A, 22B and 22C.
The eighth aspect is the tilt detection device according to the sixth aspect of the invention, wherein the tilt detecting means compares the amplitude of the first difference signal with the amplitude of the second difference signal.
The ninth aspect of the invention corresponds to off-track detection in the embodiments.
The ninth aspect is the tilt detection device according to the present invention, further comprising: off-track detecting means for outputting an off-set amount representing the amount of displacement between the center of the track and the center of the light spot, by comparing a third summed signal representing the sum of the outputs from the first and second photo detecting elements when reflected light from the first shifted pits is received by the two-split photo detector, with a fourth summed signal representing the sum of the outputs from the first and second photo detecting elements when reflected light from the second shifted pits is received by the two-split detector, the off-set amount being added to the tracking control means.
The tenth aspect of the invention corresponds to the interval between shifted pits in the embodiments.
The tenth aspect is the tilt detection device according to the present invention, wherein the first shifted pits are provided in a repeated continuous fashion, and the second shifted pits are provided in a repeated continuous fashion, consecutively to the first shifted pits.
The eleventh aspect of the invention corresponds to a case where the interval between shifted pits is small (FIG. 8) in the embodiments.
The eleventh aspect is the tilt detection device according to the tenth aspect of the invention, wherein the space Ls representing the interval at which the first shifted pits are repeated is such that Lp less than Ls less than 2Lp, where Lp is the pit length.
The twelfth aspect of the invention corresponds to a case where the interval between shifted pits is large (FIG. 9) in the embodiments.
The twelfth aspect is the tilt detection device according to the tenth aspect of the invention, wherein the space Ls representing the interval at which the first shifted pits are repeated is such that 20Lp less than Ls, where Lp is the pit length.
The thirteenth aspect of the invention corresponds to method (3) in the embodiments.
The thirteenth aspect is a tilt detection device for detecting inclination of the recording surface of an optical disc having tracks formed in such a manner that they contain periodic wobbles, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
an photo detector for receiving reflected light from said optical disc;
tracking control means for controlling the position of said light spot on a track; and
tilt detecting means for detecting inclination of the recording surface of an optical disc according to the amplitude of a wobble signal output when reflected light from the aforementioned wobbling track is received by the photo detector.
The fourteenth aspect of the invention corresponds to method (2) in the embodiments.
The fourteenth aspect is a tilt detection device for detecting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
an photo detector for receiving reflected light from said optical disc;
tracking control means for controlling the position of said light spot on a track; and
tilt detecting means for detecting inclination of the recording surface of an optical disc according to the amplitude of a tracking error signal output when reflected light from a track is received by the photo detector, provided that said tracking control means is switched off and the light spot is traversing the tracks.
The fifteenth aspect of the invention corresponds to FIG. 10 in the embodiments.
According to the fifteenth aspect, in the tilt detection device according to the present invention, tilt detection and tilt quantity sampling are performed at the inner circumference region, the middle circumference region and the outer circumference region of the optical disc. Thereby, it is possible to detect the tilt angle accurately, regardless of the radial position on the optical disc, and hence signal quality during recording and reproduction can be improved.
The sixteenth aspect of the invention corresponds to FIG. 10 in the embodiments.
Correction of the quantity of tilt is carried out if the output of the tilt detecting means is at or above a prescribed value.
The seventeenth aspect of the invention corresponds to method (1) in the embodiments.
The seventeenth aspect is an optical disc device for detecting and correcting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
a two-split photo detector for receiving light reflected from said optical disc, said photo detector including a first photodetecting element and a second photo detecting element divided in a direction parallel to the track;
tracking control means for controlling the position of said light spot on a track;
tilt detecting means for detecting inclination of the recording surface of the optical disc with respect to the optical axis of said light beam by a difference signal output representing the difference between the signals from said first and second photo detecting elements when reflected light from said continuous track is received by the two-split photo detector; and
tilt correcting means for controlling the angle of the optical disc according to the quantity of tilt detected by the tilt detecting means.
The eighteenth aspect of the invention corresponds to method (4) in the embodiments.
The eighteenth aspect is an optical disc device for detecting and correcting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
a two-split photo detector for receiving light reflected from said optical disc, said photo detector including a first photo detecting element and a second photo detecting element divided in a direction parallel to the track;
tracking control means for controlling the position of said light spot on a track;
tilt detecting means for detecting inclination of the recording surface of the optical disc, by comparing a first summed signal representing the sum of the outputs from the first and second photo detecting elements when reflected light from said first shifted pits is received by the two-split photo detector, with a second summed signal representing the sum of the outputs from the first and second photo detecting elements when reflected light from said second shifted pits is received by the two-split photo detector; and
tilt correcting means for controlling the angle of the optical disc according to the quantity of tilt detected by the tilt detecting means.
The nineteenth aspect of the invention corresponds to method (5) in the embodiments.
The nineteenth aspect is an optical disc device for detecting and correcting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
a two-split photo detector for receiving light reflected from said optical disc, said photo detector including a first photo detecting element and a second photo detecting element divided in a direction parallel to the track;
tracking control means for controlling the position of said light spot on a track;
tilt detecting means for detecting inclination of the recording surface of the optical disc, by comparing a first difference signal representing the difference between the outputs from the first and second photo detecting elements when reflected light from said first shifted pits is received by the two-split photo detector, with a second difference signal representing the difference between the outputs from the first and second photo detecting elements when reflected light from said second shifted pits is received by the two-split photo detector; and
tilt correcting means for controlling the angle of the optical disc according to the quantity of tilt detected by the tilt detecting means.
The twentieth aspect of the invention corresponds to method (3) in the embodiments.
The twentieth aspect is an optical disc device for detecting and correcting inclination of the recording surface of an optical disc having tracks formed in such a manner that they contain periodic wobbles, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
an photo detector for receiving reflected light from said optical disc;
tracking control means for controlling the position of said light spot on a track;
tilt detecting means for detecting inclination of the recording surface of an optical disc according to the amplitude of a wobble signal output when reflected light from the aforementioned wobbling track is received by the photo detector; and
tilt correcting means for controlling the angle of the optical disc according to the quantity of tilt detected by the tilt detecting means.
The twenty-first aspect of the invention corresponds to method (2) in the embodiments.
The twenty-first aspect of the invention is an optical disc device for for detecting and correcting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
an photo detector for receiving reflected light from said optical disc;
tracking control means for controlling the position of said light spot on a track;
tilt detecting means for detecting inclination of the recording surface of an optical disc according to the amplitude of a tracking error signal output when reflected light from a track is received by the photo detector, provided that said tracking control means is off and the light spot is traversing the tracks; and
tilt correcting means for controlling the angle of the optical disc according to the quantity of tilt detected by the tilt detecting means.
The twenty-second aspect of the invention corresponds to method (1) in the embodiments.
The twenty-second aspect is a tilt detection method for detecting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising the steps of:
focusing a light spot onto said optical disc;
receiving light reflected from said optical disc by a photo detector including a first photo detecting element and a second photo detecting element divided in a direction parallel to the track;
performing tracking control for controlling the position of said light spot on a track; and
detecting inclination of the recording surface of the optical disc with respect to the optical axis of said light beam by a difference signal output representing the difference between the signals from said first and second photo detecting elements when reflected light from said continuous track is received.
The twenty-third aspect of the invention corresponds to method (4) in the embodiments.
The twenty-third aspect is a tilt detection method for detecting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising the steps of:
focusing a light spot onto said optical disc;
receiving light reflected from said optical disc by a photo detector including a first photo detecting element and a second photo detecting element divided in a direction parallel to the track;
performing tracking control for controlling the position of said light spot on a track; and
detecting inclination of the recording surface of the optical disc, by comparing a first summed signal representing the sum of the outputs from the first and second photo detecting elements when reflected light from said first shifted pits is received, with a second summed signal representing the sum of the outputs from the first and second photo detecting elements when reflected light from said second shifted pits is received.
The twenty-fourth aspect of the invention corresponds to method (5) in the embodiments.
The twenty-fourth aspect is a tilt detection method for detecting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising the steps of:
focusing a light spot onto said optical disc;
receiving light reflected from said optical disc by a photo detector including a first photo detecting element and a second photo detecting element divided in a direction parallel to the track;
performing tracking control for controlling the position of said light spot on a track; and
detecting inclination of the recording surface of the optical disc, by comparing a first difference signal representing the difference between the outputs from the first and second photo detecting elements when reflected light from said first shifted pits is received, with a second difference signal representing the difference between the outputs from the first and second photo detecting elements when reflected light from said second shifted pits is received.
The twenty-fifth aspect of the invention corresponds to method (3) in the embodiments.
The twenty-fifth aspect is a tilt detection method for detecting inclination of the recording surface of an optical disc having tracks formed in such a manner that they contain periodic wobbles, comprising the steps of:
focusing a light spot onto said optical disc;
receiving reflected light from said optical disc;
performing tracking control for controlling the position of said light spot on a track; and
detecting inclination of the recording surface of an optical disc according to the amplitude of a wobble signal output when reflected light from the aforementioned wobbling track is received by the photo detector.
The twenty sixth aspect of the invention corresponds to method (2) in the embodiments.
The twenty-sixth aspect is a tilt detection method for detecting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising the steps of:
focusing a light spot onto said optical disc;
receiving reflected light from said optical disc;
performing tracking control for controlling the position of said light spot on a track; and
detecting inclination of the recording surface of an optical disc according to the amplitude of a tracking error signal output when reflected light from a track is received, provided that said tracking control means is switched off and the light spot is traversing the tracks.
The twenty-seventh aspect of the invention corresponds to FIG. 26 and FIGS. 27A, 27B, 27C and 27D in the embodiments.
The twenty-seventh aspect is a tilt detection device relating to the present invention further comprises off-track detecting means representing the off-set amount for the tracking control, by comparing the phases of the output values corresponding to the first and second shifted pits from diagonal sum signal outputs from a four-split photo detector, when reflected light from the first and second shifted pits is received by the four-split photo detector, the off-set amount being added to the tracking control means.
The twenty-eighth aspect of the invention corresponds to FIG. 26 and FIGS. 27A, 27B, 27C and 27D in the embodiments.
The twenty-eighth aspect is an optical disc device comprising:
an optical head for recording and reproducing signals by focusing a light spot onto an optical disc having tracks;
focus control means for controlling the focal position of said light spot on the surface of the optical disc;
tracking control means for controlling the position of said light spot on a track;
a four-split photo detector for receiving reflected light from said optical disc, said photo detector having four light-receiving surfaces divided by orthogonal dividing lines;
a calculating circuit for generating:
a focus error signal generated from the output of said four-split photo detector;
a tracking error signal generated from the output of said four-split photo detector;
a total sum signal generated from the output of said four-split photo detector; and
an off-track detection signal generated from two diagonal sum signals, each representing the summed outputs of two diagonally opposed photo detecting elements in said four-split photo detector;
off-track detecting means for detecting the amount of off-track from the off-track detection signal generated by said calculating circuit; and
off-track controlling means for correcting the off-track position of said light spot from the detection value detected by said off-track detecting means.
The twenty-ninth aspect of the invention corresponds to FIG. 26 and FIGS. 27A, 27B, 27C and 27D in the embodiments.
The twenty-ninth aspect of the invention is the optical disc device according to the twenty-eighth aspect of the invention, wherein the detection value detected by the off-track detecting means is detected from a reproduction signal reproduced by said optical head while passing first shifted pits and second shifted pits, said first shifted pits and the second shifted pits being displaced respectively to a first side and a second side of a track from the center of the track.
The thirtieth aspect of the invention corresponds to FIG. 26 and FIGS. 27A, 27B, 27C and 27D in the embodiments.
The thirtieth aspect is an off-track detection method for an optical disc, comprising the steps of:
recording and reproducing signals by focusing a light spot onto an optical disc having tracks;
controlling focus for controlling the focal position of said light spot on the surface of the optical disc;
performing tracking control for controlling the position of said light spot on a track;
receiving reflected light from said optical disc by a four-split photo detector, said photo detector having four light-receiving surfaces divided by orthogonal dividing lines;
performing calculations in order to generate:
a focus error signal generated from the output of said four-split photo detector;
a tracking error signal generated from the output of said four-split photo detector;
a total sum signal generated from the output of said four-split photo detector; and
an off-track detection signal generated from two diagonal sum signals, each representing the summed outputs of two diagonally opposed photo detecting elements in said four-split photo detector;
detecting the amount of off-track from the off-track detection signal generated by said calculating step; and
controlling off-track for correcting the off-track position of said light spot from the detection value detected by said off-track detecting step.
The thirty-first aspect of the invention corresponds to FIG. 26 and FIGS. 27A, 27B, 27C and 27D in the embodiments.
The thirty-first aspect of the invention is the optical disc device according to the thirtieth aspect of the invention, wherein the detection value detected by said off-track detection step is detected from a reproduction signal reproduced by said optical head while passing first shifted pits and second shifted pits, said first shifted pits and the second shifted pits being displaced respectively to a first side and a second side of a track from the center of the track.